Periodontitis is a bacteria-driven inflammatory bone loss disease affecting 47% of adults in the United States.1 We were the first to demonstrate that sphingosine-1-phosphate receptor 2 (S1PR2) plays a key role in regulating the inflammatory bone loss response.18 S1PR2, a G protein-coupled receptor, is expressed in most tissues and mammalian cells.14,15 Previous studies19,21 showed that S1PR2 controls the migration of monocytes and macrophages in response to S1P, affecting immune responses. Our previous study18 demonstrated that knockdown of S1PR2 by a specific S1PR2 shRNA significantly reduced IL-1?, IL-6, and TNF-? protein levels induced by an oral pathogen Aggregatibacter actinomycetemcomitans (Aa); suppressed osteoclastogenesis and bone resorption induced by RANKL compared with controls. Consistent with our previous study, our preliminary data have shown that inhibition of S1PR2 by its specific antagonist JTE013 significantly reduced IL- 1?, IL-6, and TNF-? protein levels induced by Aa, and suppressed osteoclastogenesis induced by RANKL compared with controls. Furthermore, treatment with S1PR2 shRNA or JTE013 suppressed chemotaxis of monocytes and macrophages induced by Aa-stimulated cell culture media. Since generation of proinflammatory cytokines, chemotaxis of inflammatory cells, and osteoclastogenesis lead to periodontal tissue damages, alveolar bone loss, and tooth loss, we hypothesize that pharmacological inhibition of S1PR2 will reduce inflammatory bone loss induced by oral pathogens and serve as a novel therapeutic strategy for periodontitis. There are several critical gaps on how S1PR2 regulates cellular signaling pathways that control oral pathogen-induced proinflammatory cytokine production, chemotaxis of monocytes and macrophages, and osteoclastogenesis. Therefore, the objective of the proposal is to elucidate the specific cellular signaling pathways regulated by S1PR2 in controlling these immune responses. Moreover, we will determine if inhibiting S1PR2 in vivo can attenuate inflammatory bone loss induced by oral pathogens. Our specific aims will determine if knockdown or inhibition of S1PR2 in vitro will 1) reduce PI3K, MAPKs, RhoA, and NF-kB induced by Aa, subsequently decreasing IL-1?, IL-6, and TNF-? production; 2) reduce the activation of PI3K induced by Aa-stimulated cell culture media, subsequently decreasing chemotaxis of monocytes and macrophages; 3) suppress podosome components (PI3K, Src, Pyk2, integrins, F-actin, integrins, paxillin, vinculin, and talin) on monocytes and macrophages induced by RANKL, subsequently suppressing osteoclastogenesis; and 4) whether pharmacological inhibition of S1PR2 in vivo can reduce inflammatory bone loss in an experimental periodontitis model induced by Aa. These studies define novel signaling pathways regulated by S1PR2 in modulating bacterial infection, chemotaxis of monocytes and macrophages, and osteoclastogenesis. Moreover, these studies will develop a novel therapeutic approach for periodontitis and other inflammatory bone loss diseases by targeting S1PR2.